B. Hoghooghi, J.M. McKittrick, E. Helsel, and O.A. Lopez, "Viscous Deformation of Glass Ceramics in Barium Aluminosilicates," in:  Proceedings of the 5th International Symposium on Ceramic Materials and Components for Engines, edited by D.S. Yan, S.R. Fu, and S.X. Shi (World Scientific, Singapore, 1995), pp. 644-647.

Near-net-shaped formed bodies of monoclinic celsian ceramics have been fabricated through viscous deformation of a glass. The celsian precursors were obtained by exchanging Ba²⁺ and Li⁺ ions for Na⁺ in a sodium aluminosilicate zeolite. Upon heat treatment the zeolite crystalline structure transforms to an amorphous phase (around 627°C). Samples were pressed above the glass transition temperature (around 900°C) under stresses of 21-30 MPa to densify the glass and a forming piece was inserted. The sample was then heated above the crystallization temperature (around 1050°C) to obtain a shaped celsian ceramic body.